1. Field of the Invention
The present invention relates to a mirror assembly for an automobile in which a position or posture of a mirror thereof is detected and adjusted electrically.
2. Description of the Related Art
Conventionally, there has been provided one type of a mirror assembly for an automobile having a mechanism for electrically detecting and adjusting a position or posture of a mirror thereof, for the purpose of realizing a better mirror position or posture which depends upon a position or posture of a driver in a car equipped with the mirror assembly (see Japanese Laid-Open Utility Model Publication No. 60-37856, for example).
On the other hand, there has been suggested another type of mirror assembly for an automobile, the general construction of which is shown in FIG. 2, which is so constructed that a mirror position detector (mirror posture detector) 4 is mounted on a rear end side of a mirror push-pull operation shaft 2 mounted on a rear side of a mirror 1. It is to be noted that FIG. 2 is a plan view, as an explanatory view, showing partially in cross section a mirror assembly for an automobile according to one embodiment of the present invention, where its basic construction is common to the construction used in the conventional mirror assembly.
With reference to FIG. 2, and FIG. 1 in which a main part, indicated by a circle, of FIG. 2 is conventional, a description is made below on the conventional mirror assembly for the automobile.
In FIG. 2, which illustrates the one embodiment of the present invention, a reference numeral 1 denotes a mirror; 3 denotes a mirror holder for holding the mirror 1 from the rear side thereof; 2 denotes a mirror push-pull operation shaft one end of which is connected to the mirror holder 3 and the other end of which has a rear end face 60; 5 denotes a rotary variable resistor for detecting an angular change of the mirror 1 as a change of value of resistance thereof; 8 denotes an actuator that is fixed to the rotary variable resistor 5 and that has a contact face 12 forming on the side of the rear end face 60 of the mirror push-pull operation shaft 2; 9 denotes a drive unit for moving the mirror push-pull operation shaft 2 in its axial direction; and 4 denotes a mirror position detector (mirror posture detector) that includes both the rotary variable resistor 5 and the actuator 8. All these parts and members are accommodated in an unshown visor.
Referring to the figure, when the mirror push-pull operation shaft 2 is driven to move axially by the drive unit 9, the mirror holder 3, which supports the mirror 1 and which is supported by a pivotal support portion, inclines universally, while the position of the mirror 1 is detected by the mirror position detector 4. The mirror holder 3 has a holding portion for holding the mirror 1 on a peripheral part of its front face, a connecting portion to which the mirror push-pull operation shaft 2 is connected on a peripheral part of its rear face, and a pivotal support portion for allowing the mirror holder 3 to universally incline about its central part.
The one end, as described above, of the mirror push-pull operation shaft 2 is connected to the mirror holder 3. With the mechanism, the mirror 1 is driven to incline when the mirror push-pull operation shaft 2 is moved axially. At this time, the other end of the mirror push-pull operation shaft 2 rotates the actuator 8 of the mirror position detector 4 with the rear surface 60 of the other end of the mirror push-pull operation shaft 2 contacting the contact surface 12 of the actuator 8 so that the position or posture of the mirror 1 is detected.
More specifically, the mirror position detector 4 is constructed as follows. That is, the actuator 8 is fixed to a rotation shaft 13 of the rotary variable resistor 5, and a center of rotation of the actuator 8 (namely, a direction in which the rotation shaft 13 extends) is perpendicular to the axial direction of the mirror push-pull operation shaft 2.
The rotary variable resistor 5 detects a change in rotational angle of the actuator 8 as a change in value of resistance. Accordingly, an axial linear displacement of the mirror push-pull operation shaft 2 is first converted into a change in rotational angle of the rotary variable resistor 5, and then the change in rotational angle of the rotary variable resistor 5 is converted into a change in value of resistance thereof.
With the mechanism, the position or posture of the mirror 1 can be detected from the change in value of resistance of the rotary variable resistor 5 in the mirror position detector 4, or from the change in rotational angle thereof.
In the conventional mechanism, a contacting part between a mirror push-pull operation shaft 102 and an actuator 108 is as follows. That is, referring to FIG. 1, a rear end face 106 of the mirror push-pull operation shaft 102 is flat in shape, and a contact face 112 of the actuator 108 is square-bar shaped or plate shaped, in which these parts 106, 112 are normally kept in contact with each other.
However, the conventional mirror assembly for the automobile shown in FIG. 1 has a following technical problem.
Namely, when the rear end face 106 of the mirror push-pull operation shaft 102 is positioned at a rear end face upper position 106a or a rear end face lower position 106b, relative to a standard position shown by a solid line in the figure, where a distance or displacement between the rear end face upper position 106a and the standard position is equal to a distance or displacement between the rear end face lower position 106b and the standard position, the actuator 108 is positioned at an actuator upper position 108a or an actuator lower position 108b, respectively, with respect to the standard position. In FIG. 1, the distance between the rear end face upper position 106a and the standard position, and the distance between the rear end face lower position 106b and the standard position, are both indicated by a displacement .DELTA..times..
In the operation, when the actuator 108 is at the actuator standard position, the contact point between the actuator 108 and the rear end face 106 of the mirror push-pull operation shaft 102 is at a contact standard position 111. Meanwhile, when the actuator 108 is at the actuator upper position 108a, the contact point between the actuator 108 and the rear end face 106 of the mirror push-pull operation shaft 102 is at a contact upper position 111a. Meanwhile, when the actuator 108 is at the actuator lower position 108b, the contact point between the actuator 108 and the rear end face 106 of the mirror push-pull operation shaft 102 is at a contact lower position 111b. In the operation, the distance between the contact upper position 111a and a center of the rotation shaft 13, is greater than the distance between the contact lower position 111b and the center thereof.
As the mirror push-pull operation shaft 102 moves axially so that the rear end face 106 thereof moves from the rear end face upper position 106a to the rear end face lower position 106b, the contact point 111 moves from the contact upper position 111a to the contact lower position 111b; namely, the contact point 111 moves over a distance corresponding to a diameter of the mirror push-pull operation shaft 102.
Provided that an angle forming between the actuator at the actuator upper position 108a and the actuator at the actuator standard position is QA, and provided that an angle forming between the actuator at the actuator lower position 108b and the actuator at the actuator standard position is QB, there is a relation QA&lt;QB therebetween; namely, the two angles are not equal to each other. This means that the actuator 108 does not rotate linearly even if the rear end face 106 of the mirror push-pull operation shaft 102 is displaced or moved linearly. In other words, even if the mirror push-pull operation shaft 102 is displaced or moved linearly, the change in value of resistance of the rotary variable resistor 5 is not linear, and the value of resistance of the rotary variable resistor 5 varies with a state in which the value of resistance thereof deviates from its expected linear change.
In order to compensate this deviation, there has been required a complex detection circuit; otherwise, resulting in a poor detection accuracy of the mirror position or posture.